Genetic parameters for ewe reproduction with objectively measured wool traits in Elsenburg Merino flock

Abstract

Reproduction is important for sustainable lamb production in Merino sheep. Data from a Merino flock maintained at Elsenburg Research Farm in the Western Cape, South Africa, were used to investigate the genetic parameters for ewe reproduction traits and their relationship with objectively measured wool traits. Traits included number of lambs born during the first lambing opportunity (NLB1), number of lambs weaned during the first lambing opportunity (NLW1), total weight of lamb weaned during the first lambing opportunity (TWW1), number of lambs born during a ewe's lifetime (NLB3), number of lambs weaned during a ewe's lifetime (NLW3), and total weight weaned per ewe's reproductive life (TWW3) Fixed effects of selection line, birth type, sex, age of the dam in years, year of birth, and the sex*birth year interaction had significant effects on all bodyweight and objectively measured wool traits. Only year of birth and selection line affected ewe reproduction traits. Heritability estimates amounted to 0.10 ± 0.03 for NLB1, 0.07 ± 0.02 for NLW1, 0.10 ± 0.04 for TWW1, 0.25 ± 0.04 for NLB3, 0.12 ± 0.03 for NLW3, and 0.18 ± 0.04 for TWW3. Wool traits were moderately heritable at 0.28 ± 0.05 (staple strength) to 0.60 ± 0.03 (clean yield (CY)) and coefficient of variation of fibre diameter (CVFD). Relationships among ewe reproduction traits were high, ranging from 0.74 between TWW1 and NLB3 to 1.00 between NLW1 and TWW1. The genetic relationships of ewe reproduction traits with wool weights and staple length were positive. Fibre diameter (FD) and CY were unfavourably related to ewe reproduction traits. It seems possible to improve ewe reproduction when selecting on NLB, NLW, and TWW in Merino sheep without unwanted correlated response to selection in wool traits, with the exception of FD and CY.______________________________________________________________________________

Relationship of ewe reproduction with subjectively assessed wool and conformation traits in the Elsenburg Merino flock

“…Ewe reproduction traits were measured at their first lambing opportunity at two years or over a threeyear period from their lambing opportunities at two to four years old. Details of selection practices applied in the flock and the husbandry and management practices applied to the experimental animals and heritability for ewe reproduction traits are fully described by Matebesi-Ranthimo et al (2017) and will not be repeated here. These traits included number of lambs born at the first lambing opportunity at approximately two years old (NLB1), number of lambs weaned at the first lambing opportunity (NLW1), total weight of lamb weaned at the first lambing opportunity (TWW1), number of lambs born from two to four years old (NLB3), number of lambs weaned from two to four years old (NLW3) and total weight of lamb weaned from two to four years old (TWW3).…”

“…The data editing for ewe reproduction traits was described by Matebesi-Ranthimo et al (2017), while that of subjectively assessed wool and conformation traits used in this investigation was performed as described in Matebesi-Ranthimo et al (2014). The ASReml program (Gilmour et al, 2009) was used to perform analyses similar to those applied by Matebesi-Ranthimo et al (2017).…”

“…The ASReml program (Gilmour et al, 2009) was used to perform analyses similar to those applied by Matebesi-Ranthimo et al (2017). Therefore, fixed effects to be included in the operational model for each trait were tested and the variance components and ratios were estimated as described in Matebesi-Ranthimo et al (2017).…”

“…These traits included number of lambs born at the first lambing opportunity at approximately two years old (NLB1), number of lambs weaned at the first lambing opportunity (NLW1), total weight of lamb weaned at the first lambing opportunity (TWW1), number of lambs born from two to four years old (NLB3), number of lambs weaned from two to four years old (NLW3) and total weight of lamb weaned from two to four years old (TWW3). These traits, NLB1, NLW1, TWW1, NLB3, NLW3 and TWW3 were expressed per lambing opportunity (Matebesi-Ranthimo et al, 2017). Subjective traits were assessed according to a linear scale ranging from 1 to 50 (Table 1; Olivier et al, 1987) at 11 to 12 months old as described by Matebesi et al (2009a).…”

“…Research on these relationships is essential to assess putative correlated responses in ewe reproduction when selection is based on subjectively assessed wool and confirmation traits. A companion paper (Matebesi-Ranthimo et al, 2017) assessed the relationships of ewe reproduction with objectively measured traits using the same Merino resource flock. Therefore, the aim of this study is to investigate the relationships of ewe reproduction with subjectively assessed wool and conformation traits in South African Merino sheep.…”